Diffractive waveplate lenses and applications

ABSTRACT

Methods, systems and devices for diffractive waveplate lens and mirror systems allowing electronically pointing and focusing light at different focal planes. The system can be incorporated into a variety of optical schemes for providing electrical control of transmission. In another embodiment, the system comprises diffractive waveplates of different functionality to provide a system for controlling not only focusing but other propagation properties of light including direction, phase profile, and intensity distribution. The diffractive waveplate lens and mirror systems are applicable to optical communication systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/220,995 filed Dec. 14, 2018, now allowed, which is a Continuation ofU.S. patent application Ser. No. 14/688,425 filed Apr. 16, 2015, nowU.S. Pat. No. 10,191,191, which claims the benefit of priority to U.S.Provisional Application Ser. No. 61/980,062 filed Apr. 16, 2014, andU.S. patent application Ser. No. 16/220,995 filed Dec. 14, 2018, nowallowed, which is a Continuation-In-Part of U.S. patent application Ser.No. 14/688,197 filed Apr. 16, 2015, now U.S. Pat. No. 10,274,650, whichclaims the benefit of priority to U.S. Provisional Patent ApplicationSer. No. 61/980,062 filed Apr. 16, 2014, and U.S. patent applicationSer. No. 14/688,197 filed Apr. 16, 2015 now U.S. Pat. No. 10,274,650, isa Continuation-In-Part of U.S. patent application Ser. No. 13/916,627filed Jun. 13, 2013, Abandoned, which is a Continuation of U.S. patentapplication Ser. No. 12/697,083 filed Jan. 29, 2010, Abandoned. Theentire disclosure of the applications listed in this paragraph areincorporated herein by specific reference thereto.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under Contract No.W911QY-12-C-0016. The government has certain rights in this invention.

FIELD OF INVENTION

This invention relates to optical lenses, the method of theirfabrication, applications of the lenses, and applications ofcombinations of said lenses with application of said lenses includingimaging optics and systems, astronomy, displays, polarizers, opticalcommunication and other areas of laser and photonics technology.

BACKGROUND AND PRIOR ART

The present invention is in the technical field of optics. Moreparticularly, the present invention is in the technical field of lenses.Lenses are commonly made by shaping an optical material such as glass.The weight of such lenses increases strongly with diameter making themexpensive and prohibitively heavy for applications requiring large area.Also, the quality of a lens typically decreases with increasing size. Toachieve desired features such as high-quality imaging, conventionallenses sometimes have curved surfaces that are non-spherical. The needto grind and polish conventional lenses with non-spherical surfaces canmake such lenses extremely expensive. Segmented lenses such as Fresnellenses are relatively thin, however, the structural discontinuitiesresult in severe aberrations. Uses of holographic lenses are limited bythe compromise of efficiency, spectral bandwidth and dispersion. Thus,there is a need for lenses that could be obtained in the form of thinfilm structurally continuous coatings on a variety of substrates.

Thus, the need exists for solutions to the above problems with the priorart.

SUMMARY OF THE INVENTION

The objective of the present invention is providing a lens withcontinuous thin film structure whose properties can be changed in auseful way by application of an electrical potential to the lens.

The second objective of the present invention is providing a combinationof lenses with spherically symmetric continuous thin film structure suchthat the properties of the individual lenses are changed by means of theapplication of an electrical potential, in such a way that thecombination of lenses allows the focal position of an imaging system tobe adjusted among a multiplicity of possible focal positions.

The third objective of the present invention is providing combinationsof lenses, each with a continuous thin film structure, such that one ormore of the lenses are controlled by means of the application of anelectrical potential, and such that by means of electrical switching ofthese lenses, coupling between optical fibers can be turned on or off.

The fourth objective of the present invention is providing a variableattenuator of electromagnetic radiation using an electrically-controlledthin-film structure.

Many of the exemplary applications have been described herein with termssuch as “light” being used to describe the electromagnetic radiationthat is acted upon by the disclosed diffractive waveplate lenses. Theterm “light” in this context should not be taken to restrict the scopeof the disclosed embodiments to only those in which the electromagneticradiation acted upon or manipulated by the diffractive waveplate lensesis in the visible region of the spectrum. As will be evident to thoseskilled in the art, the exemplary embodiments disclosed here, inaddition to being applicable in the visible region of the spectrum, areequally applicable to the microwave, infrared, ultraviolet, and X-rayregions of the spectrum. Exceptions to this generalization are theapplications relating to human vision, for which operation in thevisible region of the spectrum is required.

The design and function of the optical lenses of the present inventionhave not been suggested, anticipated or rendered obvious by any of theprior art references.

Further objects and advantages of this invention will be apparent fromthe following detailed description of the presently preferredembodiments which are illustrated schematically in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows spatial distribution of optical axis orientation inspherical diffractive waveplate lenses of one sign.

FIG. 1B shows spatial distribution of optical axis orientation inspherical diffractive waveplate lenses of an opposite sign.

FIG. 2A shows a representation of a spherical diffractive waveplate lenswith continuous alignment lines of anisotropy axis of the birefringentmaterial.

FIG. 2B shows spherical diffractive waveplate lenses of opposite signsin description with continuous alignment lines.

FIG. 3 shows a diffractive waveplate lenses viewed from opposite sides.

FIG. 4A shows polarization properties of focusing and defocusing of aright-hand circular polarized beam by a diffractive waveplate lens,respectively.

FIG. 4B shows polarization properties of focusing and defocusing aleft-hand circular polarized beam by a diffractive waveplate lens,respectively.

FIG. 5A shows the structure of a cylindrical diffractive waveplate lensof one handedness.

FIG. 5B shows the structure of a cylindrical diffractive waveplate lensof opposite handedness.

FIG. 6A shows a lens with spherical aberration focusing light to a largefocal spot.

FIG. 6B shows a lens, with spherical aberration corrected, focusinglight to a small focal spot.

FIG. 6C shows a multilayer system of diffractive waveplate lenses ofvarying spatial frequency of optical axis orientation and differentarea.

FIG. 6D shows a lens with aberrations corrected with a diffractivewaveplate coating.

FIG. 7 shows a pair of diffractive diffractive waveplate lenses focusinglight to the same spot for right hand circular (RHC) polarization aswell as left hand circular (LHC) polarization.

FIG. 8 shows a system of a triplet of diffractive waveplate lensesfocusing light to the same spot for light of RHC polarization or LHCpolarization, said system having the same effective focal length foreither polarization.

FIG. 9A shows a conventional glass lens focusing light in the red regionof the spectrum to a small focal spot.

FIG. 9B shows the paths of rays of light in the red region of thespectrum, and light in the blue region of the spectrum, near the focusof a glass lens, illustrating the fact that light with differentwavelengths is focused to different axial locations by the glass lens.

FIG. 10A shows a combination of one glass lens and three diffractivewaveplate lenses focusing light in the red region of the spectrum to asmall focal spot.

FIG. 10B shows the paths of rays of light in the red region of thespectrum, and light in the blue region of the spectrum, near the focusof the combination of one glass lens and three diffractive waveplatelenses, illustrating the fact that light with different wavelengths isfocused to the same axial location by said combination of lenses.

FIG. 11A shows the focusing of a collimated beam of light by anelectrically switchable diffractive waveplate lens, with the lens in theactive state (electric field off).

FIG. 11B shows the lack of focusing of a collimated beam of light by anelectrically switchable diffractive waveplate lens, with the lens in thepassive state (electric field on).

FIG. 12A shows the focusing of a collimated beam of light by acombination of a conventional refractive lens and two electricallyswitchable lenses. with both diffractive waveplate lenses in the activestate (electric field off).

FIG. 12B shows the focusing of a collimated beam of light by acombination of a conventional refractive lens and two electricallyswitchable lenses, with the first diffractive waveplate lens in thepassive state (electric field on), and the second diffractive waveplatelens in the active state (electric field off).

FIG. 12C shows the focusing of a collimated beam of light by acombination of a conventional refractive lens and two electricallyswitchable lenses, with the second diffractive waveplate lens in thepassive state (electric field on), and the first diffractive waveplatelens in the active state (electric field off).

FIG. 12D shows the focusing of a collimated beam of light by acombination of a conventional refractive lens and two electricallyswitchable lenses, with both diffractive waveplate lenses in the passivestate (electric field on).

FIG. 13A shows the focusing of the output of an optical fiber into theinput of another optical fiber by means of a combination of threeelectrically switchable diffractive waveplate lenses, with all threelenses in the active state (electric field oft).

FIG. 13B shows the absence of focusing of the output of an optical fiberinto the input of another optical fiber by means of a combination ofthree electrically switchable diffractive waveplate lenses, with allthree lenses in the passive state (electric field on).

FIG. 13C shows the tip of an optical fiber outputting both focused anddefocused beams with the proportion between them being set by apolarization control element at the input of the fiber.

FIG. 14A shows a system of diffractive waveplates interspaced withpolarization control elements for switching the focus of the beam todifferent spots in space.

FIG. 14B shows a switchable system comprising variety of diffractivewaveplate structures.

FIG. 14C shows a system for switching the orientation of a light beamintensity distribution with cylindrical diffractive waveplates.

FIG. 15 shows a diffractive waveplate lens deposited on one of thesubstrates of the switchable phase retarder.

FIG. 16 shows a flat mirror comprising a switchable phase retarder and adiffractive waveplate lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining the disclosed embodiments of the present invention indetail it is to be understood that the invention is not limited in itsapplications to the details of the particular arrangements shown sincethe invention is capable of other embodiments. Also, the terminologyused herein is for the purpose of description and not of limitation.

In the Summary above and in the Detailed Description of PreferredEmbodiments and in the accompanying drawings, reference is made toparticular features (including method steps) of the invention. It is tobe understood that the disclosure of the invention in this specificationincludes all possible combinations of such particular features. Forexample, where a particular feature is disclosed in the context of aparticular aspect or embodiment of the invention, that feature can alsobe used, to the extent possible, in combination with and/or in thecontext of other particular aspects and embodiments of the invention.and in the invention generally.

In this section, some embodiments of the invention will be describedmore fully with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown, This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will convey the scope of the invention to those skilled inthe art. Like numbers refer to like elements throughout, and primenotation is used to indicate similar elements in alternativeembodiments.

A list of components will now be described.

-   101 left hand thin film diffractive waveplate lens-   102 right hand thin film diffractive waveplate lens-   201 continuous lines-   300 plane-   301 observer-   302 observer-   400 component/element-   410 right-hand circular polarized (RHCP) light beam-   411 defocused RHCP light beam-   412 focused RHCP light beam-   420 left-hand circular polarized (LHCP) light beam-   421 defocused (LHCP) light beam-   422 focused LHCP beam-   430 DWL layer-   440 substrate-   601 collimated lens beams-   602 lens-   603 focal region-   612 aspheric lens-   613 focal region-   614 diffractive waveplate lens-   615 diffractive waveplate lens-   616 diffractive waveplate lens-   617 incoming beam-   618 conventional lens-   619 diffractive waveplate lens-   620 focal region-   701 collimated beam-   702 optical system axis-   703 right-hand circular polarized beam-   704 left-hand circular polarized beam-   711 diffractive waveplate lens-   712 diffractive waveplate lens-   721 focal region-   801 diffractive waveplate lens-   802 diffractive waveplate lens-   803 diffractive waveplate lens-   804 cone of light-   805 focal point-   901 collimated beam-   902 optical system axis-   903 spherical lens-   904 RHCP component-   905 LHCP red beam-   906 focal point-   907 RHCP component of blue light-   908 LHCP component of blue light-   909 focal point-   1001 diffractive waveplate lens-   1002 diffractive waveplate lens-   100 diffractive waveplate lens-   1010 focal point-   1101 collimated light beam-   1102 optical system axis-   1103 diffractive waveplate lens-   1104 focal point-   1120 non-diffracted collimated beam-   1105 focused beam-   1120 non-diffractive collimated beam-   1201 beam-   1202 axis-   1203 lens-   1204 diffractive waveplate lens-   1205 diffractive waveplate lens-   1210 focal plane-   1220 focal plane-   1230 focal plane-   1240 focal plane-   1301 fiber optic-   1302 tip of 1301-   1303 light cone-   1304 diffractive waveplate lens-   1305 diffractive waveplate lens-   1306 diffractive waveplate lens-   1307 converging cone-   1308 tip of 1309-   1309 fiber optic-   1310 beam block-   1311 diverging beam-   1320 fiber optic-   1321 diffractive waveplate lens-   1322 defocused beam-   1323 focused beam-   1401 diffractive waveplate lens-   1402 diffractive waveplate lens-   1403 diffractive waveplate lens-   1404 polarization switching components-   1405 cycloidal diffractive waveplate-   1406 vector vortex waveplate-   1407 cylindrical diffractive waveplate lens-   1408 cylindrical diffractive waveplate lens-   1409 polarization switching components (switchable phase retardation    layer)-   1410 polarization switching components (switchable phase retardation    layer)-   1411 cylindrical diffractive waveplate lens-   1412 cylindrical diffractive waveplate lens-   1501 electrodes for application of electric field-   1502 substrate-   1503 substrate-   1504 electro-optical material-   1505 diffractive waveplate film-   1602 diffractive waveplate film-   1603 variable phase retardation film-   1604 mirror-   1605 focused beam

Glossary of Terms:

Diffractive waveplates (DWs): A birefringent film with anisotropy axisorientation modulated in the plane of the film. Different modulationpatterns are possible resulting in different optical functionality,including lens, prism, axicon, etc. Generally, DWs may possess more thanone layer, and the anisotropy axis may be modulated also in the bulk ofthe layer.

Diffractive waveplate lens: A diffractive waveplate with lens function.It may provide spherical, cylindrical, and other types of lens action.

Optical substrate or optical film A transparent material providingmechanical support for DWs. It may be glass, quartz, plastic, or anyother material that is at least partially transparent for thewavelengths of light that propagate through the DWs. It may possessanti-reflective or anti-scratch functions.

Switchable Diffractive waveplate: A DW that can be switched betweendiffractive and non-diffractive states upon application of externalinfluences such as electric fields, temperature, optical radiation, etc.Generally, the switching can take place through gradual change ofdiffraction spectrum.

Variablephase retarder or polarization controller: An optical componentcapable of controlling the polarization of light propagated through itby applying electric fields, changing temperature, exposure to a lightbeam, etc. Particularly, it may be a liquid crystal sandwiched betweensubstrates coated with transparent electrodes.

Before explaining the disclosed preferred embodiments of the presentinvention in detail it is to be understood that the invention is notlimited in its application to the details of the particular arrangementsshown since the invention is capable of other embodiments. Also, theteiininology used herein is for the purpose of description and notlimitation.

In the description here of the invention, the term “light” will often beused to describe the electromagnetic radiation that interacts with thediffractive waveplate lenses that are subject of this invention.Although “light” generally means electromagnetic radiation with awavelength in the visible region of the electromagnetic radiation with awavelength in the visible region of the electromagnetic spectrum, itshould be understood that the usage of the term “light” in thedescription is not restrictive, in the sense of limiting the design andapplication to diffractive waveplate lenses that operate only in thevisible region of the spectrum. In general, all the designs and conceptsdescribed herein apply to operation over a wide range of theelectromagnetic spectrum, including the microwave, infrared, visible,ultraviolet, and X-ray regions. While physical embodiments ofdiffractive waveplate lenses are at present advanced for operation inthe visible region of the spectrum, the designs and applicationsdisclosed here are applicable over all the noted regions of theelectromagnetic spectrum.

The present invention relates to the design and application ofdiffractive waveplate lenses. The term “diffractive waveplate lens” asused herein describes a thin film of birefringent material deposited ona transparent structure, for example, a thin flat substrate of opticalmaterial such as glass. This birefringent film has the property that itretards the phase of light of one linear polarization by approximatelyone half wave (pi radians of optical phase) relative to the light of theother linear polarization. In diffractive waveplate lenses, the opticalaxis orientation depends on the transverse position on the waveplate,i.e. the position in the two coordinate axes perpendicular to thesurface of the diffractive waveplate lens. In other words, the opticalaxis orientation is modulated in one or both of the transversedirections parallel to the surface of the substrate on which the activethin film is applied. Lensing action is due to parabolic profile ofoptical axis orientation modulation.

There are two general types of diffractive waveplate lenses to which thepresent invention applies. The first type of diffractive waveplate lensis axially symmetric and is used, for example, to focus a collimatedbeam of light to a point in space. The second type of diffractivewaveplate lens is cylindrically symmetric and is used, for example, tofocus a collimated beam of light to a line segment in space. In manyexamples below, an optical system of circular symmetry is used as anexample, but in general, all of the conclusions apply as well to opticalsystems of cylindrical symmetry.

In FIG. 1, the orientation of the anisotropy axis at each point of thebirefringent thin film 101 is indicated by a short line segments. In thefirst type of diffractive waveplate lenses to which the presentinvention applies, illustrated in FIG. 1A, the orientation of theanisotropy axis of the birefringent material comprising the thin filmlayer depends only on the radial distance r from a center point. Thistype of spherical diffractive waveplate lens is used for applicationssuch as focusing a collimated beam of light to a point for imaging adistant scene onto a sensor array. To perform this function, the angle athat the anisotropy axis of the birefringent material makes with thecoordinate axis is given by the following equation:

$\alpha = {{\pm \frac{k_{0}}{4f}}r^{2}}$

where k₀=2π/λ is the wavenumber of the light that is to be focused bythe diffractive waveplate lens, λ is the wavelength of that radiation, fis the focal length of the diffractive waveplate lens (DWL), and r isthe distance to the central point.

The difference in signs in variation of the anisotropy axis with radiusdesignate lenses of two opposite signs. The difference in correspondingpatterns 101 and 102 in FIG. 1 is even better visible in representationof the DWL structure by continuous lines 201 as shown in FIG. 2A. DWLsof different signs correspond to the right- and left-spiraling patternsin FIG. 2B.

In the preferred embodiment of the present invention, DWLs of oppositeoptical axis modulation signs need not be two separate opticalcomponents and is obtained by rotating the DWL around an axis in theplane of the DWL by 180 degrees. The observers 301 and 302 looking at agiven DWL from opposite sides in FIG. 3 see patterns of opposite sign.

This optical asymmetry is described in detail in FIG. 4 wherein the DWLlayer 430 is shown on a substrate 440. As an example, a right-handcircular polarized (RHCP) light beam 410 is transformed into a defocusedleft-hand circular polarized (LHCP) beam 421 when incident from the sideof the substrate. Arranging the component 400 with the substrate facingthe incident RHCP beam results in a focused LHCP beam 422.

For a LHCP light beam 420 in FIG. 4, the situation is reversed. The LHCPbeam 420 is transformed into a focused RHCP beam 412 when incident fromthe side of the DWL and it is transformed into defocused RHCP beam 411when incident from the side of the substrate.

In the second type of diffractive waveplate lenses to which the presentinvention applies, illustrated in FIG. 5, the orientation of the opticalaxis of the birefringent material comprising the thin film layer dependsonly on the linear distance x from a central axis. This type ofcylindrical diffractive waveplate lens is used for applications such asfocusing a beam of light to a line for imaging light from the sun onto aline of photovoltaic devices. In the paraxial approximation, the angle □that the optical axis of the birefringent material makes with thecoordinate axis is given by the following equation:

$\alpha = {{\pm \frac{k_{0}}{4f}}r^{2}}$

where k₀ and f have the same meanings as before, and x is the distancefrom the center of the coordinate axis. FIGS. 5A and B correspond topatterns of different sign (cylindrical lenses of different sign).

One of the problems with conventional lenses is spherical aberration,illustrated in FIG. 6A and FIG. 6B, in which an incident collimated beam601 is focused by a lens 602.

When a refractive material such as glass foiined such that one or bothsurfaces closely approximates a section of a sphere, such as the lens602, then the resulting structure can be used to focus light asillustrated in FIG. 6A. However, as is well known in the art, whenfocused by a lens constructed in this way, the rays of light from adistant source are not all brought to the same focal point.Specifically, such a lens with spherical surfaces will bring theperipheral rays, the rays at the edge of the beam, to a focus closer tothe lens than the point to which the lens brings the rays closer to theaxis. Hence, the rays in the focal region 603 in FIG. 6A do not all passthrough the same point. This phenomenon is called spherical aberration.

By means of modifying one of the surfaces of a lens such that thesurface is not spherical (i.e. such that the surface is aspherical), allincident light in a collimated beam can be brought to the same focalpoint, as indicated in FIG. 6B. With an appropriately designed asphericlens 612, all the rays in the focal region 613 pass through the samepoint. However, fabrication of such aspheric lenses is often veryexpensive, and therefore their use is impractical for many applications.

A major advantage of diffractive waveplate lenses is that the focusingeffect of aspheric surfaces of arbitrary form can be produced simply bychanging the dependence of optical axis orientation of the birefringentfilm with coordinate a=ax+bx²+cx²+ . . . . For such lenses, unlike thesituation with conventional lenses, the manufacturing expense of a lensthat has no spherical aberration will not be significantly greater thanfor a lens that does have spherical aberration.

Another technique for obtaining nonlinear orientation modulation patterncomprises stacking layers of diffractive waveplate lenses with varyingmodulation patterns and varying degree of overlap. A system of threesuch layers, 614, 615, and 616 is shown in FIG. 6C.

In one of the embodiments shown in FIG. 60, the thin film diffractivewaveplate lens 619 may be deposited on a conventional lens 618 tocorrect for aberrations and focus an incoming beam 617 onto the samepoint in space 620.

In general, the optical deflection angle resulting from a light beampropagating through a diffractive waveplate lens depends on the circularpolarization of the light. As a result, if the focal length of a lenssuch as the ones illustrated in FIG. 1 is f for right-hand-circularpolarized (RHCP) light as an example, then the focal length of the samelens for left-hand-circular polarized (LHCP) light will be −f.Therefore, a diffractive waveplate lens that converges a collimated beamof RHCP light will diverge a beam of LHCP light. This is illustrated bythe action of the diffractive waveplate lens 711 in FIG. 7, in which anincident collimated beam 701, centered on axis 702, and including both aRHCP component and a LHCP component, converges the RHCP component 703and diverges the LHCP component 704 of the incident beam.

In many applications, one of the functions of the optical system is tobring light to a focal point (in the case of an axially symmetricsystem) or to a focal line (in the case of a cylindrically symmetricsystem). It is often desirable for light of all polarizations to bebrought to the same focal point or focal line. In the case ofdiffractive waveplate lenses, for which the focal length of a singlelens for LHCP light is opposite in sign to the focal length for the samelens for RHCP light, it is possible to bring light of both polarizationsto the same focal point or focal line by the use of two diffractivewaveplate lenses. In the preferred embodiment the focal lengths of thetwo lenses are related as

${f_{2}} = {{f_{1}} - \frac{d^{2}}{f_{1}}}$

where the distance between the two lenses d is smaller than the absolutevalue of the focal length of the 1^(st) lens, d<|f₁|. By that, the backfocal length f_(BFL) of the system of two lenses, the distance of thefocal spot from the second lens, is determined by equation

$f_{BFL} = {\frac{f_{1}^{2}}{d} - d}$

For example, the distance between diffractive waveplate lens 711 anddiffractive waveplate lens 712 can be 50 mm, the focal lengths of lenses711 and 712 for RHCP light 703 can be 70.7 mm and −35.4 mm,respectively. Therefore, the focal lengths of lenses 711 and 712 forLHCP light 704 are −70.7 mm and 35.4 mm, respectively. As shown in FIG.7, this combination of focal lengths and spacings results in both RHCPlight 703 and LHCP light 704 being brought to the same focal point 721.

As will be evident to those skilled in the art, if an optical systembrings light of both RHCP and LHC polarization to a single point or linefocus, then it will bring light of any polarization to the same point orline focus. Therefore FIG. 7 demonstrates the ability with twodiffractive waveplate lenses to bring light in any polarized orunpolarized beam to the same point or line focus.

As previously noted, for diffractive waveplate lenses of the type thatis the subject of the present invention, the sign of focal length forLHC polarized light is opposite to that of the focal length for RHCpolarized light. It was shown by means of FIG. 7 and the associateddiscussion that despite the difference in focal length for light of thetwo possible circular polarizations, it is possible to focus light ofany polarization with a combination of two diffractive waveplate lenses.However, there may be some applications that an alternative method maybe used to focus light of both polarizations, using only a singlediffractive waveplate lens and an additional optical element. Forexample, instead of using two diffractive waveplate lenses, a singlediffractive waveplate lens combined with a waveplate and a refractivelens made from a birefringent material could also be used to performfocusing of light of any polarization. Methods of combining diffractivewaveplate lenses into optical systems that include such waveplates andbirefringent refractive elements will be evident to anyone skilled inthe art of optical design, once the fundamental characteristics ofdiffractive waveplate lenses of this invention are revealed.

As will be evident to those skilled in the art, the effective focallength (EFL) of the optical system comprising lens 711 and 712 in FIG. 7is much different for light of RHC polarization than it is for light ofLHC polarization. In some applications, it is required that light of allpolarizations be focused with the same EFL. The capability of acombination of three diffractive waveplate lenses to not only bringlight of any polarization to the same point or line focus, but also tohave the same EFL for light of any polarization, is illustrated in FIG.8. As in FIG. 7, in FIG. 8 an incident beam 701 symmetrically disposedabout a system optical axis 702, comprising both a RHCP component 703and a LHCP component 704, is incident on the optical system. However, inFIG. 8, the optical system now consists of three lenses 801, 802, and803, with a spacing of 30 mm between adjacent lenses, and with focallengths of 70.7 mm, −35.4 mm, and 45.5 mm, respectively. As shown inFIG. 8, this combination of three diffractive waveplate lenses bringsboth the RHCP component 703 and the LHCP component 704 of the incidentbeam to the same focal point 805. While in both FIG. 7 and FIG. 8 bothpolarization components of the incident light beam 701 are brought tothe same focal point, the significant difference between the two figuresis that in FIG. 8, the cone angle of the cone of light 804 thatconverges to the focus 805 is the same for both the RHC component 703and the LHC component 304, as must be the case if and only the systemEFL is the same for both components. FIG. 8 therefore demonstrates thatwith three diffractive waveplate lenses, light of any polarization canbe brought to the same focal point, with the same EFL.

Due to the diffractive nature of diffractive waveplate lenses, thedeflection angle for a given grating is a function of wavelength, inaccordance with the well-known transmission grating diffractioncondition, d sin θ=mλ. Here d is the grating spacing, θ is the anglethrough which the grating deflects the beam, m is the order ofdiffraction, and λ is the wavelength. The phase gratings used indiffractive waveplate lenses are designed to be continuous in nature,eliminating all but the first orders of diffraction. Also, forillustrative purposes, it is useful to consider only the paraxial case,in which the angle through which the beam is diffracted is smallcompared with π, in which case sin can be approximated by θ. Theequation above therefore becomes dθ≈λ. That is, in the paraxialapproximation, the deflection angle of a ray of light incident on alocal area of a diffractive waveplate lens is directly proportional tothe wavelength of the light. As a direct consequence, the focal lengthof the lens is inversely proportional to wavelength.

Because of this strong dependence of the focal length of a diffractivewaveplate lens on wavelength, such lenses may be used to correct forchromatic aberration in optical systems containing refractive elements.Chromatic aberration, as the expression is used here, is the dependenceof the focal position on wavelength. Due to the dependence of the indexof refraction n of any dielectric medium on wavelength, every imagingsystem that employs such media suffers from chromatic aberration.

To illustrate the ability of diffractive waveplate lenses to correct forchromatic aberration, a specific example will be used. FIG. 9Aillustrates an imaging system employing a single refractive element madewith BK7 glass, an optical material available from Schott AdvancedOptics. A collimated beam 901 of white light from a distant source isincident on spherical lens 903 with aperture centered on axis 902.Although BK7 is isotropic, and therefore does not act any differently onRHCP light than it acts on LHCP light, we will distinguish between thesetwo components of the incident unpolarized light because later in thisdiscussion, diffractive waveplate lenses will be considered whoseeffects differ between these two polarization components. With only therefractive element made from BK7 in place, both the RHCP component 904and the LHCP component 905 of the red component of the white input beamare brought to the same focal point 906.

The BK7 material from which the refractive lens in FIG. 9A is made hasan index of refraction of n=1.515 for red light (wavelength λ=650 nm)and n=1.526 for blue light (wavelength λ=450 nm). As a result, the focallength of the lens is slightly shorter for blue light than it is for redlight. This is shown in FIG. 9B, showing a magnified view of the regionnear the focal point. The focal point 909 on the axis 902 of the inputbeam, for both the RHCP component of the blue light 907 and the LHCPcomponent of the blue light 908, is 2.2% closer to the lens than thefocal point 906 for the two polarization components of the red light.

For optical systems such as cameras, it is undesirable for the focalpositions at any two wavelengths within the operating wavelength band todiffer significantly. Therefore, chromatic aberration correction is animportant part of the design of such optical systems. The most commonapproach to chromatic aberration correctio in refractive imaging systemsis to include refractive elements of multiple types, with variousindices of refraction and various dependences of index of refraction onwavelength. These approaches increase the complexity and cost of thesystem. Therefore, there is a need for alternative approach to chromaticaberration correction.

FIG. 10A illustrates correction of the chromatic aberration in aconventional refractive lens by employment of a set of three diffractivewaveplate lenses. As was the case for FIGS. 9A and 9B, white lightcollimated beam 901 is incident along an axis 902 onto the conventionalBK7 glass lens 903. FIG. 10A includes three diffractive waveplate lenses1001, 1002, and 1003. As is evident from the figure, the path of redlight through the combined system is slightly different for the RHCPcomponent 904 than it is for the LHCP component 905, but both of thepolarization components of the red light are brought to the same focalpoint 1010. The focal lengths of the lenses shown in the figure for RHCPpolarized red light are 10.00 mm, 14.00 mm, −7.00 mm, and 14.07 mm forlenses 903, 1001, 1002, and 1003, respectively. As noted previously, forthe diffractive waveplate lenses, the focal lengths change sign for LHCpolarized light.

FIG. 10B shows the ability of the lens combination illustrated in FIG.10A to correct for chromatic aberration. The focal positions 906 and 909for red and blue light, respectively, before the addition of diffractivewaveplate lenses 1001, 1002, and 1003, are shown in FIG. 10B forreference. Light of all four considered polarization/wavelengthcombinations is brought to the same focal point 1010 after the additionof lenses 1001, 1002, and 1003. In FIG. 10B, the paths of the RHC redbeam 904, LHC red beam 905, RHC blue beam 907, and LHC blue beam 908 areshown slightly offset vertically for clarity, but for the consideredoptical design, the four beams come to exactly the same focal point1010.

In the discussion of FIG. 6 it was noted that by adjusting the gratingspacing in a diffractive waveplate lens, spherical aberration can beeliminated. In the discussion of FIG. 10 it was demonstrated thatchromatic aberration correction of a refractive imaging system ispossible by the addition of appropriate diffractive waveplate lenses.Once the mechanism of correcting for spherical aberration alone, and themechanism for correcting for chromatic aberration alone, methods will beevident to those skilled in the art that allow the use of diffractivewaveplate lenses to be used to simultaneously compensate for bothspherical and chromatic aberration.

Switchable Lens

It is well known that the optical properties of liquid crystal baseddevices can be made to be controllable by means of an electric fieldacross the medium containing the liquid crystal material. A commonexample of this is the LCD (liquid crystal display) used in computermonitors and television displays. Diffractive waveplate lenses can beconstructed such that the focusing properties can be turned on and offby means of the application of an electric potential across the device.An example of such a device is illustrated in FIG. 11. In FIG. 11A, withno electric field applied, an incident collimated beam 1101 enters adiffractive waveplate lens 1103 centered on axis 1102 of the opticalsystem, and is focused by the lens to focal point 1104. In FIG. 11 B,due to the effect of an applied electric field, the orientation of theliquid crystal molecules in lens 1103 is changed in such a way that thebeam is no longer focused by the lens, and the output beam 1120 remainscollimated.

1. Electrically Tunable Focusing System Electrically Tunable FocusingSystem

One of the potential applications of such switchable diffractivewaveplate lenses is to provide a purely electronic means of focusing foran optical imaging system, without the need to move any opticalelements. This would be highly desirable in some applications because iteliminates the cost, weight, and reliability issues of mechanicalactuators in the focusing system. One of the many possible embodimentsof such an electronic focusing system wherein a combination of twoelectrically switchable diffractive waveplate lenses is used to providefour distinct focus positions is illustrated in FIG. 12. FIG. 12A showsthe case in which a beam 1201 is incident on the input aperture centeredalong axis 1202, and is focused to a point in focal plane 1210 by acombination of lenses 1203, 1204, and 1205. In FIG. 12A both of thediffractive waveplate lenses, 1204 and 1205, are turned on so they bothpull the focal position towards the lens system FIG. 12B is the same asFIG. 12A except that in FIG. 12B, lens 1205 remains on but lens 1204 hasbeen shut off. This results in the focal point shifting from focal plane1210 to focal plane 1220. FIG. 12C is also the same as FIG. 12A exceptthat in FIG. 12C, lens 1204 remains on but lens 1205 has been shut off.This results in the focal point shifting from focal plane 1210 to focalplane 1230. FIG. 12D is also the same as FIG. 12A except that in FIG.12D, both lens 1204 and lens 1205 have been shut off. This results inthe focal point shifting from focal plane 1210 to focal plane 1240.

In the design concept illustrated in FIG. 12A, four different focalpositions are accessible by means of switching two lenses on and off.This is accomplished by using diffractive waveplate lenses of differentfocal power. By this means, in general, with k switchable lenses, 2^(k)distinct focus positions can be made accessible, particularly, equallyspaced. Each lens may have twice the focal power of the previous one,for example.

Camera Lens

An example of uses of electrically switchable diffractive waveplatelenses of the present invention are camera lenses and machine visionwherein the contrast reduction due to presence of defocused beam doesnot affect required image information obtained due to focused portion ofthe beam,

Fiber Illuminator/Focusing Switching System

An important use of diffractive waveplate lenses in the currentinvention are polarization maintaining fibers. As an example, thediffractive waveplate lens coated at the output facet of the fiber mayallow collimating or focusing the light emerging from the fiber. Thus,changing the state of polarization of a laser light injected into afiber would allow, for example, switching the light at its outputbetween illuminating state used for imaging and focused state that maybe used for example, for surgery.

Fiber Coupler

The capability to switch a diffractive waveplate lens from an active toa passive state makes possible many other applications in which opticalbeams are manipulated by a switchable lens. One of these manyapplications is the switching on and off of optical coupling between theoutput from one optical fiber and the input of another optical fiber.

Such optical switching is illustrated in FIG. 13A and FIG.13B. In FIG.13A, light from the tip 1302 of optical fiber 1301 expands away from thetip within a light cone 1303 characteristic of the fiber type. Thisoutput light is captured and focused by the diffractive waveplate lenses1304, 1305, and 1306. Except for a small fraction of the light in theconverging cone 1307 of the light beam, all the light is focused intothe tip 1308 of a second optical fiber 1309. A small fraction of thelight is blocked because it impinges on a beam block 1310, but almostall the light goes around the beam block and reaches fiber tip 1308.

As indicated in FIG. 13A, due to the specific arrangement of thediffractive waveplate lenses 1304, 1305, and 1306, light of both RHC andLHC polarization is captured and focused into fiber 1309. As will beevident to those skilled in the art, the fact that both RHC and LHCpolarized light is captured and focused into fiber 1309 implies thatlight of any polarization emanating from fiber tip 1302 will be capturedand focused by the lens combination comprised of lenses 1304, 1305, and1306.

Although a specific exemplary arrangement of the lenses is shown in FIG.13A, it will be evident to those skilled in the art that it is ingeneral true that by appropriate selection of lens spacing and focallengths, a combination of three lenses can always be found to couple theradiation from one fiber to another for any spacing between the fibertips, and for any wavelength. The specific arrangement used as anexample in FIG. 13A is for a spacing from fiber tip 1302 to lens 1304 of1 mm, a spacing between each adjacent pair of lenses of 0.5 mm, a focallength of diffractive waveplate lenses 1304 and 1306 of 0.58 mm for RHClight, and a focal length of diffractive waveplate lens 1305 for RHClight of −0.43 mm.

Switching off the coupling from fiber 1301 to fiber 1302 is accomplishedby turning off the three lenses 1304, 1305, and 1306. The resultingoptical configuration after the three lenses are switched off is shownin FIG. 13B. The cone of light 1307 that emerges from the combination oflenses is now diverging beam 1311 instead of converging, and no lightreaches the input tip 1308 of fiber 1309.

2. Partially Focused Beams Partially Focused Beams

The transition of diffractive waveplate lenses such as lenses 1304,1305, and 1306 in FIG. 13A and FIG. 13B from the “on” state (i.e.focusing or defocusing the input beam) to the “off” state (i.e. passingthe beam without deflection) can be converted into a continuous process,such that an arbitrary and selectable fraction of the optical power inthe beam can be deflected by the diffractive structure of thediffractive waveplate lens, and the balance of the optical power in thebeam can be passed without deflection. This is accomplished by applyingan electric potential to the diffractive waveplate lens that results inan optical retardation of one linear polarization relative to the otherof more than zero retardation (at which no beam deflection occurs), butless than one-half wave of retardation (at which 100% of the opticalpower in the beam is deflected by the diffractive structure). Byappropriately adjusting the magnitude of the applied electric potential,the fraction of power focused or defocused by the lens can be adjustedto any value between 0% and 100%, For example, in the fiber couplingembodiment shown in FIG. 13A and FIG. 13B, the fraction of the powertransferred from fiber 1301 to fiber 1309 can be varied from 0% tonearly 100%. In other words, the gradual transition of the lenses fromthe state in which they do not deflect the beam at all, to the state inwhich they deflect 100% of the optical power in the beam, results in avariable optical attenuator.

In a preferred embodiment shown in FIG. 13C the diffractive waveplatelens 1321 is coated at the output facet of a fiber 1320 to split theoutput beam between focused 1323 and defocused 1322 beams controlled bythe polarization of light at the input of the fiber.

Switching from Non-Focusing to Focusing State

In one realization of the present invention, the phase retardation ofthe lens is chosen to fulfil full-wave condition wherein diffraction,hence, focusing action of the lens is absent. Application of an electricfield reduces the phase retardation to half-wave condition thus settingin the lensing action. Instead of the electric field, switching can beinduced also by temperature, light, and other influences that changeeither the order parameter or orientation of the liquid crystaldiffractive waveplate lens.

In another preferred embodiment, the initial non focusing state isobtained by arrangement of at least two diffractive waveplate lenses.Switching at least one of the lenses in such a system transforms it intoa focusing state.

Switching Diffractive Waveplate Lens System by Polarization Modulators

As an alternative to switching focusing properties of diffractivewaveplate lenses, the focus position of a light beam at the output of asystem of diffractive waveplate lenses can be controlled by usingvariable phase retardation plates to switch the polarization handednessof a beam at the output of diffractive waveplate lenses as shown in FIG.14. By switching the handedness of polarization, the focusing powers ofsubsequent lenses, 1401, 1402 and 1403, in the example shown in FIG.14A, can be added or subtracted from each other focusing an input beamto different points in space. Moreover, diffractive waveplates ofdifferent functionalities can be combined in series with polarizationswitching components 1404. As shown in FIG. 14B, the optical system cancombine, for example, a DW lens 1401, a cycloidal diffractive waveplate1405, and vector vortex waveplates 1406 along with diffractive waveplatelenses, to switch not only focus position, but propagation direction andthe phase profile of the beam as well.

In a preferred embodiment, cylindrical diffractive waveplate lenses canbe sequenced with polarization switching components 1404 to obtain abeam of different orientation of ellipticity axis. FIG. 14C shows suchan opportunity for a horizontal and vertical alignment of the beamintensity distribution profile obtained when focusing with cylindricallenses. The cylindrical diffractive waveplate lenses 1407 and 1408 areidentical in this embodiment. The cylindrical diffractive waveplatelenses 1411 and 1412 are also identical but aligned perpendicular to theorientation of the lenses 1407 and 1408. Each pair is interspaced withpolarization switching components 1409 and 14010, for example a liquidcrystal switchable phase retardation layer to generate eitherundiffracted or diffracted/focused beams.

In a preferred embodiment, the switchable phase retarder serves assubstrate for the diffractive waveplate film 1505 as shown in FIG. 15.The switchable phase retarder is comprised of substrates 1502 and 1503with transparent electrodes for application of an electric field 1501,and the electro-optical material in-between 1504 such as a liquidcrystal.

While all of the exemplary embodiments discussed herein are of arealization of diffractive waveplate lenses employed in a mode in whichthe optical beam is transmitted through the thin film diffractivewaveplate lens and through the underlying substrate, an alternativeembodiment is to apply the thin film diffractive waveplate lens to aflat mirror as demonstrated in FIG. 16. In this manner. flat reflectiveoptical elements can be fabricated to have a wide variety of beamdeflecting properties, including the ability to focus light with a flatreflective optical element. In one of the preferred embodiments shown inFIG. 16, a flat mirror 1604 comprises a variable phase retardation film1603 and a diffractive waveplate lens 1602. A circular polarizedcollimated light beam 1601 may thus be reflected from the system as afocused beam 1605, for example.

The exemplary embodiments described herein have assumed eitherexplicitly or implicitly that the thin film constituting the diffractivewaveplate lens is applied to the flat surface of a solid substrate suchas glass. Neither the assumption of a solid substrate, nor theassumption of a flat surface, should be taken as restrictive in definingthe potential embodiments of this invention. As will be evident toanyone skilled in the art, the coatings may be applied to curvedsubstrates, and to flexible substrates. All of the exemplary embodimentsdescribed herein could also be realized with either a curved substrate,a flexible substrate, or a substrate that is both curved and flexible.

Microwave, Infrared, Ultraviolet, and X-Ray Regions of the Spectrum

By merely changing the thickness of the layer, in a preferred embodimentof current invention, diffractive waveplate lenses are optimized for usein different parts of the spectrum, spanning microwave and to shortwavelengths.

While the invention has been described, disclosed, illustrated and shownin various twits of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

We claim:
 1. An optical communication system comprising: a light source;a flat mirror; a quarter wave plate deposited on the flat mirror; asystem of one or more diffractive waveplates with switchable opticalpower for receiving the light from the light source, said one or morediffractive wave plates are selected from a group consisting ofdiffractive waveplate lenses, cycloidal diffractive waveplates, axialdiffractive waveplates, axicon diffractive waveplates, beam shapingdiffractive waveplates, and arrays of diffractive waveplates; and one ormore switching devices for selectively switching the propagationdirection, phase profile, and optical power of said system of one ormore diffractive waveplates to provide an electrically controlleddiffraction property in reflected light; wherein the flat mirror and theone or more diffractive waveplates and the one or more switching devicesform the basis of an optical communication system.
 2. The opticalcommunication system as in claim 1 wherein said light source is fibercoupled.
 3. The optical communication system as in claim 1, wherein saidone or more diffractive waveplates have an optical axis orientation thatis modulated in one or both transverse directions parallel to asubstrate.
 4. The optical communication system as in claim 1 whereinsaid one or more switching devices for selectively switching the opticalpower of said optical communication system include variable phaseretardation plates.
 5. The optical communication system as in claim 4wherein said one or more diffractive waveplates are deposited on asurface of at least one of the variable phase retardation plates.
 6. Theoptical communication system as in claim 1, wherein a cylinder axes inalternating cylindrical diffractive waveplate lenses are rotated withrespect to each other.
 7. An optical communication system with multiplefocal points comprising: a generally unpolarized and non-monochromaticlight source; a system of one or more diffractive waveplates withswitchable optical power for receiving the light from the generallyunpolarized and non-monochromatic light source, said one or morediffractive wave plates are selected from a group consisting ofdiffractive waveplate lenses, cycloidal diffractive waveplates, axialdiffractive waveplates, axicon diffractive waveplates, beam shapingdiffractive waveplates, and arrays of diffractive waveplates; asubstrate in the optical communication system; and one or more switchingdevices for selectively switching the propagation direction, phaseprofile and optical power of said one or more diffractive waveplates,wherein the one or more diffractive waveplates and the substrate and theone or more switching devices provide controls for the opticalcommunication system.
 8. The optical communication system as in claim 7wherein said one or more switching devices for selectively switching atleast one of: the propagation direction, phase profile and the opticalpower of said optical communication system include variable phaseretardation plates.
 9. The optical communication system as in claim 1wherein said one or more switching devices switch said one or morediffractive wave plates from an active state to a passive state so thatoptical beams are manipulated by the said one or more switching devices.10. The optical communication system as in claim 1, wherein the lightsource is selected from the group consisting of: visible region,microwave region, infrared region, ultraviolet region and X-ray regionsof the light spectrum.
 11. The optical communication system as in claim7 wherein said one or more switching devices switch said one or morediffractive wave plates from an active state to a passive state so thatoptical beams are manipulated by the said one or more switching devices.12. The optical communication system as in claim 7, wherein thegenerally unpolarized and non-monochromatic light source is selectedfrom the group consisting of: visible region, microwave region, infraredregion, ultraviolet region and X-ray region of the light spectrum.